Current elevator installations are equipped with a safety system comprising a safety circuit. This consists of a plurality of switch contacts, which are connected in series, of different safety elements for shaft, door and cable monitoring. Opening one of these switch contacts has the consequence that the entire safety circuit is interrupted. This in turn causes interruption of power supply for the main drive and thus adoption of a rest state. For maintenance purposes or test purposes of the elevator installation individual ones or several of these switch contacts have to be bridged over by means of bridging-over elements. In the case of travel to a buffer it is necessary, for example, for a limit switch to be bridged over so as to be able to travel beyond the travel range, which is permissible in normal operation, in the shaft onto the buffer. Before the elevator installation can resume its normal operation all bridging-over elements would have to be removed from the safety circuit. However, it cannot be excluded that a maintenance engineer forgets to remove a bridging-over element again. Accordingly, reliability of the safety circuit is impaired, since a bridged-over switch contact in a given case may be unable to interrupt the safety circuit.